Cybernetics Ideas from a Thermostat:

The thermostat is a simple device that is often used to describe the basic ideas of Cybernetics. Cybernetics is the art of steering. Simply put, a goal is identified and the “system” acts to get closer to the goal. In the example of the thermostat, the user specifies the setpoint for the thermostat such that when the temperature goes below the setpoint, it kicks on the furnace and stops when the internal temperature of the house meets the desired temperature. In a similar fashion, when the temperature goes above a setpoint, the thermostat kicks on the air conditioner to bring down the internal temperature. The thermostat acts as a medium for achieving a constant temperature inside the house. This is also the idea of homeostasis. In order to achieve what the thermostat does, it needs to have a closed loop. It needs to read the internal temperature at specified frequencies, and act as needed depending upon this information. If it was an open loop, no information is fed back into the system, and thus no homeostasis is achieved. An example of an open loop is a campfire without anyone to manage it. The fire continues to burn until it goes out.

Ernst von Glasersfeld, the father of radical constructivism, talked about these ideas in his short paper, Reflections on Cybernetics (2000):

The good old thermostat, the favorite example in the early literature of cybernetics, is still a useful explanatory tool. In it a temperature is set as the goal-state the user desires for the room. The thermostat knows nothing of the room or of desirable temperatures. It is designed to eliminate any discrepancy between a set reference value and the feedback it receives from its sensory organ, namely the value indicated by its thermometer. If the sensed value is too low, it switches on the heater, if it is too high, it switches on the cooling system. Employing Gordon Pask’s clever distinction (Pask, 1969, p.23–24): from the user’s point of view, the thermostat has a purpose for, i.e. to maintain a desired temperature, whereas the purpose in the device is to eliminate a difference.

The idea that the thermostat’s purpose is simply to eliminate a difference is most important here. I have written about this here.

Von Galsersfeld continues:

This example may also help to clarify a second cybernetic feature that is rarely stressed. Imagine a thermostat that has an extremely sensitive thermometer. If it senses a temperature that is a fraction below the reference value, it switches on the heater. The moment the temperature begins to rise above the reference, it switches on the cooling system –and thus it enters into an interminable oscillation. This would hardly be desirable. Therefore, it is important to design the device so that it has an area of inaction around the reference value where neither the one nor the other response is triggered. In other words, rather than a single switching point, there have to be two, with some space for equilibrium in between.

Homeostasis does not refer to a fine line it needs to maintain. It is often a band or a range. The wider the band, the easier it is to maintain homeostasis. It is more efficient to define the “stable conditions” to be between a range of values. A good example for this is a bicycle lane. It is not easy, if not impossible, to ride a bicycle in a straight line. However, it is easy to ride a bicycle in a somewhat wider lane. With the thermostat, this region is sometimes referred to as a “deadband.” This is the range of the temperature, within which the thermostat does not act (stays OFF). Below the lower limit, the thermostat will kick on the furnace, and above the upper limit, the thermostat will kick on the air conditioner.

Another important lesson from a thermostat is that if you want to change the room temperature, there is no point in moving the thermostat value to an extreme setpoint. Let’s say that you want to cool the room down. It is of no use if you put the thermostat value at 40 degrees F (4.44 degrees C). The house will not get colder faster with this approach. The thermostat controls the temperature inside the house, but not the speed with which it achieves this.  

To be economically efficient, the thermostat must be aligned with the external temperature. For example, in colder weather conditions, the heat setpoint should be reduced (for example 67 degrees F or 19.4 degrees C), and similarly during warmer weather conditions the cool set point should be raised. Even though, the thermostat is the regulator, the user determines how this regulation is achieved. The thermostat as a regulator must also follow the Good Regulator Theorem. All good regulators must be a model of the system that it tries to regulate. The model of how to maintain the internal temperature constant (within the deadband) is programmed into the thermostat. It also follows the law of Requisite Variety. The thermostat must have the requisite variety to adjust the internal temperature based on the external perturbations. The thermostat must be able to differentiate the states of “below the setpoint temperature” or “above the setpoint temperature” to achieve the requisite variety and maintain the internal temperature. Both the Good Regulator Theorem and the Law of Requisite Variety are at utmost importance in Cybernetics, and they are both the contributions of one of the pioneers of Cybernetics, Ross Ashby.

I will finish this with some great aphorisms from Ross Ashby:

The drive to equilibrium forces the emergence of intelligence.

That the brain matches its environment is no more surprising than the matching of the two ends of a broken stick.

Every piece of wisdom is the worst folly in the opposite environment. Change the environment to its opposite and every piece of wisdom becomes the worst of folly.

The rule for decision is: Use what you know to narrow the field as far as possible: after that, do as you please.

Any system that achieves appropriate selection (to a degree better than chance) does so as a consequence of information received.

Please maintain social distance and wear masks. Stay safe and Always keep on learning…

In case you missed it, my last post was The Toyota House – Why Jidoka and JIT?

4 thoughts on “Cybernetics Ideas from a Thermostat:

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